“Band Operation of Guided-Wave Light Modulators with Filter-Type Coplanar Electrodes”, IEICE TRANS. ELECTRON., VOL. E78-C, No. 1, January 1995 discloses a optical phase modulator using so-called ACPS electrodes. In this modulator, a channel optical waveguide is formed between a ground electrode and a signal electrode of the ACPS electrodes, and a voltage is impressed on the optical waveguide, thereby modulating the phase of propagating light.
On the other hand, Japanese Patent Publication No. H2-269309A describes, in FIG. 9, that, in an amplitude modulator modulating the amplitude of incident light, a modulation voltage is impressed from asymmetric coplanar electrodes on a pair of branched waveguides of a Mach-Zehnder optical waveguide. In this type of electrodes, the respective widths of pair of gaps are different from each other.
Japanese Patent Publication No. 2005-91698A describes that, in an amplitude modulator modulating the amplitude of incident light, a modulation voltage is impressed from asymmetric coplanar electrodes on a pair of branched waveguides of a Mach-Zehnder optical waveguide. As a result, electric field intensities applied to the pair of branched waveguide are made different from each other, resulting in difference in the phase shifts caused by the modulation between light beams propagating through the respective branched waveguides. An object thereof is to obtain, as a result, a chirp characteristic.
Japanese Patent Publication No. 2004-219600A discloses that in CPW and ACPS Mach-Zehnder optical modulators, by setting a ratio of W/G, which is a ratio of the width W of a signal electrode to a gap G between a ground electrode and the signal electrode to 0.8 or more, and more preferably 2.5 or more, the electrode propagation loss can be reduced.